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Experiment-corrected milk fat C18:1 cis-9 concentrations as energy status indicator in dairy cows
Jorjong, S. ; Knegsel, A.T.M. van; Hostens, M. ; Lannoo, F. ; Opsomer, G. ; Fievez, V. - \ 2016
Cross-validation of milk fat C15:1 cis-9 as biomarker for neative energy status in early lactating cows: comparison of fixed vs. experiment-corrected cut-off values
Jorjong, S. ; Knegsel, A.T.M. van; Kemp, B. ; Fievez, V. - \ 2015
In vivo and in vitro effects of a blend of essential oils on rumen methane mitigation
Castro-Montoya, J. ; Peiren, N. ; Cone, J.W. ; Zweifel, B. ; Fievez, V. ; Campeneere, S. De - \ 2015
Livestock Science 180 (2015). - ISSN 1871-1413 - p. 134 - 142.
The effect of Agolin Ruminant, a blend of essential oils, on methane (CH4) emissions were investigated in two in vivo experiments and in four in vitro experiments. In the in vivo experiments, four lactating dairy cows and four beef heifers were supplemented 0.2 g/d of the essential oils (ca. 2–4 ppm m/v) during an eight-weeks period, where the first two weeks served as control (no essential oils supplementation). In dairy cattle, essential oils tended to decrease the daily CH4 emissions (g/d) and CH4 relative to dry matter intake (g/kg DMI) by 15% and 14%, respectively, after 6 weeks of supplementation (P=0.07), but no difference was observed for CH4 relative to milk production (g/kg milk) (P=0.64) or CH4 relative to bodyweight (g/kg BW) (P=0.12). In the in vivo experiment with beef cattle daily CH4 emissions and CH4 relative to DMI did not change when supplemented the essential oils at a dose of 0.2 g/d (numerical decreases of 10 and 11% for g CH4/d and g CH4/kg DMI, respectively) but CH4 relative to body weight tended to decrease by 20% after 6 weeks of supplementation (P=0.07). The in vitro experiments were expected to replicate the results observed in vivo. However, no decrease in CH4 production was observed in 24 h batch incubations at concentrations up to 30 ppm (m/v). A longer contact time between the essential oils (15 and 30 ppm) and the feedstuff (essential oils added ca. 16 h prior the start of the incubation) did not elicit any effect on CH4 production and was not different from addition immediately prior to the start of the incubation. Longer incubation time (96 h and 14 d) and regular supply of both substrate and additive in a consecutive batch incubation system did not induce CH4 inhibition up to essential oils doses of 30 ppm (m/v) and hence, also were not able to replicate in vivo results. Using the gas production technique (GPT) methane was inhibited by 17% with an essential oils dose of 30 ppm after 24 h, but this decrease was not constant across all times during the 72 h incubation. The blend of essential oil was effective reducing daily emissions of methane in dairy cattle and emissions relative to body weight in beef cattle, interestingly, these effects were not observed in vitro regardless of the techniques used to replicate in vivo results. This might be due to differences in the mode of action of the essential oils in vitro and in vivo, which merits attention for future research.
Milk fatty acids as possible biomarkers to diagnose hyperketonemia in early lactation
Jorjong, S. ; Knegsel, A.T.M. van; Verwaeren, J. ; Bruckmaier, R.M. ; Baets, B. De; Kemp, B. ; Fievez, V. - \ 2015
Journal of Dairy Science 98 (2015)8. - ISSN 0022-0302 - p. 5211 - 5221.
detect subclinical ketosis - beta-hydroxybutyrate concentrations - dairy-cows - energy-balance - reproductive-performance - dry period - elevated concentrations - transition period - cattle - chain
The aim of this study was to assess the potential of milk fatty acids as diagnostic tool for hyperketonemia of 93 dairy cows in a 3 × 2 factorial arrangement. Cows were fed a glucogenic or lipogenic diet and originally were intended to be subjected to a 0-, 30-, or 60-d dry period. Nevertheless, some of the cows, which were intended for inclusion in the 0-d dry period group, dried off spontaneously. Milk was collected in wk 2, 3, 4, and 8 of lactation for milk fat analysis. Blood was sampled from wk 2 to 8 after parturition for ß-hydroxybutyrate (BHBA) analysis. Cases were classified into 2 groups: hyperketonemia (BHBA =1.2 mmol/L) and nonhyperketonemia (BHBA
Milk fatty acids as possible biomarkers to early diagnose elevated concentrations of blood plasma nonesterified fatty acids in dairy cows
Jorjong, S. ; Knegsel, A. van; Verwaeren, J. ; Val Lahoz, M. ; Bruckmaier, R.M. ; Baets, B. De; Kemp, B. ; Fievez, V. - \ 2014
Journal of Dairy Science 97 (2014)11. - ISSN 0022-0302 - p. 7054 - 7064.
northeastern united-states - propylene-glycol - early-lactation - energy-balance - beta-hydroxybutyrate - metabolic predictors - displaced abomasum - culling risk - dry period - cattle
Most cows encounter a state of negative energy balance during the periparturient period, which may lead to metabolic disorders and impaired fertility. The aim of this study was to assess the potential of milk fatty acids as diagnostic tools of detrimental levels of blood plasma nonesterified fatty acids (NEFA), defined as NEFA concentrations beyond 0.6 mmol/L, in a data set of 92 early lactating cows fed a glucogenic or lipogenic diet and subjected to 0-, 30-, or 60-d dry period before parturition. Milk was collected in wk 2, 3, 4, and 8 (n = 368) and blood was sampled weekly from wk 2 to 8 after parturition. Milk was analyzed for milk fatty acids and blood plasma for NEFA. Data were classified as “at risk of detrimental blood plasma NEFA” (NEFA =0.6 mmol/L) and “not at risk of detrimental blood plasma NEFA” (NEFA
Validation of a predictive model for diagnosis of high concentration of plasma non-esterified fatty acids and subclinical ketosis in dairy cows
Jorjong, S. ; Knegsel, A. van; Verwaeren, J. ; Baets, B. De; Kemp, B. ; Fievez, V. - \ 2014
Effect of dry period length and dietary energy source on energy balance, milk yield, and milk composition of dairy cows
Knegsel, A.T.M. van; Remmelink, G.J. ; Jorjong, S. ; Fievez, V. ; Kemp, B. - \ 2014
Journal of Dairy Science 97 (2014)3. - ISSN 0022-0302 - p. 1499 - 1512.
subsequent lactation - bovine somatotropin - metabolic status - transition cows - holstein cows - fatty-acids - performance - reproduction - management - profiles
The objective of this study was to evaluate the effects of dry period length and dietary energy source in early lactation on milk production, feed intake, and energy balance (EB) of dairy cows. Holstein-Friesian dairy cows (60 primiparous and 108 multiparous) were randomly assigned to dry period lengths (0, 30, or 60 d) and early lactation ration (glucogenic or lipogenic), resulting in a 3 × 2 factorial design. Rations were isocaloric and equal in intestinal digestible protein. The experimental period lasted from 8 wk prepartum to 14 wk postpartum and cows were monitored for milk yield, milk composition, dry matter intake (DMI), energy balance, and milk fat composition. Prepartum average milk yield for 60 d precalving was 13.8 and 7.7 ± 0.5 kg/d for cows with a 0- and 30-d dry period, respectively. Prepartum DMI and energy intake were greater for cows without a dry period and 30-d dry period, compared with cows with a 60-d dry period. Prepartum EB was greater for cows with a 60-d dry period. Postpartum average milk yield until wk 14 was lower for cows without a dry period and a 30-d dry period, compared with cows with a 60-d dry period (32.7, 38.7, and 43.3 ± 0.7 kg/d for 0-, 30-, and 60-d dry period, respectively). Postpartum DMI did not differ among treatments. Postpartum EB was greater for cows without a dry period and a 30-d dry period, compared with cows with a 60-d dry period. Young cows (parity 2) showed a stronger effect of omission of the dry period, compared with a 60-d dry period, on additional milk precalving (young cows: 15.1 kg/d; older cows: 12.0 kg/d), reduction in milk yield postcalving (young cows: 28.6 vs. 34.8 kg/d; older cows: 41.8 vs. 44.1 kg/d), and improvement of the EB postcalving (young cows: 120 vs. -93 kJ/kg0.75·d; older cows: -2 vs. -150 kJ/kg0.75·d. Ration did not affect milk yield and DMI, but a glucogenic ration tended to reduce milk fat content and increased EB, compared with a more lipogenic ration. Reduced dry period length (0 and 30 d) increased the proportion of short- and medium-chain fatty acids in milk fat and omitting the dry period decreased the proportion of long-chain fatty acids in milk fat. In conclusion, shortening and omitting the dry period shifts milk yield from the postpartum to the prepartum period; this results in an improvement of the EB in early lactation. An increased energy status after a short dry period can be further improved by feeding a more glucogenic ration in early lactation.
|Dynamics on methanogenic population, protozoa numbers and rumen fermentation in response to dietary supplementation of coconut of krabok oil
Panyakaew, P. ; Goel, G. ; Yuangklang, C. ; Schonewille, J.T. ; Hendriks, W.H. ; Boon, N. ; Fievez, V. - \ 2013
In: Book of Abstracts of the 38th Animal Nutrition Research Forum, 21 May 2013, Roeselare, Belgium. - Roeselare : KATHO - p. 35 - 35.
|Milk fatty acids as possible biomarkers to diagnose high levels of blood nonesterified fatty acids and subclinical ketosis at an early stage in the beginning of lactation
Jorjong, S. ; Knegsel, A.T.M. van; Verwaeren, J. ; Val Lahoz, M. ; Baets, B. De; Kemp, B. ; Fievez, V. - \ 2013
In: Book of Abstracts of the 38th Animal Nutrition Research Forum, 21 May 2013, Roeselare, Belgium. - Roeselare : KATHO - p. 27 - 27.
Incubation of selected fermentable fibres with feline faecal inoculum: correlations between in vitro fermentation characteristics and end products
Rochus, K. ; Bosch, G. ; Vanhaecke, L. ; Velde, H. van de; Depauw, S. ; Xu, J. ; Fievez, V. ; Wiele, T. van der; Hendriks, W.H. ; Janssens, G.P.J. ; Hesta, M. - \ 2013
Archives of Animal Nutrition 67 (2013)5. - ISSN 1745-039X - p. 416 - 431.
gas-production kinetics - chain fatty-acids - dietary fiber - domestic cat - human gut - substrate - feces - food - progression - propionate
This study aimed to evaluate correlations between fermentation characteristics and end products of selected fermentable fibres (three types of fructans, citrus pectin, guar gum), incubated with faecal inocula from donor cats fed two diets, differing in fibre and protein sources and concentrations. Cumulative gas production was measured over 72 h, fermentation end products were analysed at 4, 8, 12, 24, 48 and 72 h post-incubation, and quantification of lactobacilli, bifidobacteria and bacteroides in fermentation liquids were performed at 4 and 48 h of incubation. Partial Pearson correlations, corrected for inoculum, were calculated to assess the interdependency of the fermentation characteristics of the soluble fibre substrates. Butyric and valeric acid concentrations increased with higher fermentation rates, whereas acetic acid declined. Concentrations of butyric acid (highest in fructans) and propionic acid were inversely correlated with protein fermentation end products at several time points, whereas concentrations of acetic acid (highest in citrus pectin) were positively correlated with these products at most time points. Remarkably, a lack of clear relationship between the counts of bacterial groups and their typically associated products after 4 h of incubation was observed. Data from this experiment suggest that differences in fibre fermentation rate in feline faecal inocula coincide with typical changes in the profile of bacterial fermentation products. The observed higher concentrations of propionic and butyric acid as a result of fibre fermentation could possibly have beneficial effects on intestinal health, and may be confounded with a concurrent decrease in the production of putrefactive compounds. In conclusion, supplementing guar gum or fructans to a feline diet might be more advantageous compared with citrus pectin. However, in vivo research is warranted to confirm these conclusions in domestic cats.
Effect of supplementing coconut or krabok oil, rich in medium-chain fatty acids on ruminal fermentation, protozoa and archaeal population of bulls
Panyakaew, P. ; Boon, N. ; Goel, G. ; Yuangklang, C. ; Schonewille, J.T. ; Hendriks, W.H. ; Fievez, V. - \ 2013
Animal 7 (2013)12. - ISSN 1751-7311 - p. 1950 - 1958.
different hypervariable regions - gradient gel-electrophoresis - myristic acid - in-vitro - methane suppression - ciliate protozoa - energy-balance - lauric acid - dairy-cows - rumen
Medium-chain fatty acids (MCFA), for example, capric acid (C10:0), myristic (C14:0) and lauric (C12:0) acid, have been suggested to decrease rumen archaeal abundance and protozoal numbers. This study aimed to compare the effect of MCFA, either supplied through krabok (KO) or coconut (CO) oil, on rumen fermentation, protozoal counts and archaeal abundance, as well as their diversity and functional organization. KO contains similar amounts of C12:0 as CO (420 and 458 g/kg FA, respectively), but has a higher proportion of C14:0 (464 v. 205 g/kg FA, respectively). Treatments contained 35 g supplemental fat per kg DM: a control diet with tallow (T); a diet with supplemental CO; and a diet with supplemental KO. A 4th treatment consisted of a diet with similar amounts of MCFA (i.e. C10:0+C12:0+C14:0) from CO and KO. To ensure isolipidic diets, extra tallow was supplied in the latter treatment (KO+T). Eight fistulated bulls (two bulls per treatment), fed a total mixed ration predominantly based on cassava chips, rice straw, tomato pomace, rice bran and soybean meal (1.5% of BW), were used. Both KO and CO increased the rumen volatile fatty acids, in particular propionate and decreased acetate proportions. Protozoal numbers were reduced through the supplementation of an MCFA source (CO, KO and KO+T), with the strongest reduction by KO. Quantitative real-time polymerase chain reaction assays based on archaeal primers showed a decrease in abundance of Archaea when supplementing with KO and KO+T compared with T and CO. The denaturing gradient gel electrophoresis profiles of the rumen archaeal population did not result in a grouping of treatments. Richness indices were calculated from the number of DGGE bands, whereas community organization was assessed from the Pareto–Lorenz eveness curves on the basis of DGGE band intensities. KO supplementation (KO and KO+T treatments) increased richness and evenness within the archaeal community. Further research including methane measurements and productive animals should elucidate whether KO could be used as a dietary methane mitigation strategy.
Rumen degradation of oil palm fronds is improved through pre-digestion with white rot fungi but not through supplementation with yeast or enzymes
Hassim, H.A. ; Lourenco, M. ; Goh, Y.M. ; Baars, J.J.P. ; Fievez, V. - \ 2012
Canadian Journal of Animal Science 92 (2012)1. - ISSN 0008-3984 - p. 79 - 87.
vitro fermentation characteristics - in-vitro - rice straw - chemical-composition - fibrolytic enzymes - wheat-straw - metabolism - degradability - digestibility - culture
Rumen fermentation kinetics of oil palm fronds (OPF) supplemented or not with enzymes (Hemicell® or Allzyme SSF®) or yeasts (Levucell®SC or Yea-Sacc®) were studied through an in vitro gas production test (96 h) (exp. 1). In exp. 2, enzymes were supplemented to OPF pre-treated during 3 or 9 wk with either one of five white rot fungi strains. Yeasts and enzymes were tested both in active and inactive forms, which revealed the most appropriate set-up to distinguish between the rate of supplements as direct contributors to the fermentation substrate vs. stimulators of the fermentation of the basal substrate. In exp 1, addition of active and inactive Yea-Sacc® increased the apparently rumen degradable carbohydrates (ARDC) by 11%, whereas enzymes did not affect rumen degradability of non-inoculated OPF. Neither yeast nor enzymes influenced the rate of gas production of non-inoculated OPF, except for active Hemicell® at the low dose. In exp. 2, inoculation of OPF with Ceriporiopsis subvermispora for 3 wk and Lentinula edodes for 9 wk increased ARDC, but additional enzyme supplementation did not further improve ARDC or the rate of gas production.
Effects of condensed tannins from Salix varieties on methanogenesis in vitro
Faure, P.A.Z. ; Lourenco, M. ; Mueller-Harvey, I. ; Falchero, L. ; Pellikaan, W.F. ; Fievez, V. - \ 2012
In: Proceedings of the 37th Animal Nutrition Research Forum, Wageningen, The Netherlands, 18 April 2012. - Wageningen : Wageningen University - p. 55 - 56.
Causes of variation in fatty acid content and composition in grass and maize silages
Khan, N.A. ; Cone, J.W. ; Fievez, V. ; Hendriks, W.H. - \ 2012
Animal Feed Science and Technology 174 (2012)1. - ISSN 0377-8401 - p. 36 - 45.
lipid-metabolism - perennial ryegrass - milk-composition - cutting date - fresh grass - dairy-cows - nitrogen - forages - fertilization - senescence
The aim of this study was to quantify the variation in fatty acid (FA) content and composition in grass and maize silages and to identify key management factors during plant growth and the ensiling process that cause this variation. Samples of grass (n = 101) and maize (n = 96) silages were randomly collected from commercial dairy farms in The Netherlands in 2007 and 2008. Multivariate analysis was computed on data related to agronomic conditions, harvest-maturity, wilting management (grass only), chemical composition and feeding value of the individual silages to search for variables which cause the variation in FA contents. Total FA content was highly variable in grass (8.10–32.47 g/kg DM) and maize (12.37–35.25 g/kg DM) silages, and contents of all major individual FA also had a high variation. The content of C18:3n-3 had large variation (3.57–20.53 g/kg DM) in grass silages, while C18:2n-6 had large variation (6.89–22.41 g/kg DM) in maize silages. Redundancy analysis (i.e., a combination of principal components analysis and multiple regression) showed that variables related to plant maturity at harvest explained most of the variation in FA content, with silages from young grass and young maize having high contents of C18:3n-3. Plant cell wall components and digestibility are related to the maturity at harvest and were strong predictors of the FA contents in grass and maize silages. Regression equations based on nutrient composition provided relatively good estimations of the contents of C18:3n-3 (R2 = 0.73) and total FA (R2 = 0.65) in grass silages. Regression equations based on nutrient composition and feeding values gave relatively good estimations of the contents of C18:2n-6 (R2 = 0.51) and total FA (R2 = 0.48) in maize silages. Bruising (i.e., removing of the waxy layer of leaves and stem), silage pH and ammonia–N content did not affect the FA content in the grass silages
Improving ruminal degradability of oil palm fronds using white rot fungi
Rahman, M.M. ; Lourenco, M. ; Hassim, H.A. ; Baars, J.J.P. ; Sonnenberg, A.S.M. ; Cone, J.W. ; Boever, J.L. de; Fievez, V. - \ 2011
Animal Feed Science and Technology 169 (2011)3-4. - ISSN 0377-8401 - p. 157 - 166.
in-vitro digestibility - chemical-composition - wheat-straw - cattle feed - substrate - fermentation - lignin - waste - plant
The use of oil palm fronds (OPF) in livestock production is limited as up to 0.20 of their dry biomass is lignin. White rot fungi (WRF) are very effective basidiomycetes for biological pre-treatment as they degrade lignin extensively. Ten WRF were screened for their potential to increase OPF digestibility, which were colonized with one of the 10 WRF for 3 or 9 wks at 30 °C. After colonization, weight loss, neutral detergent fiber, acid detergent fiber, lignin(pm), cellulose, crude protein and ash were determined. Further, in vitro gas production was determined using rumen fluid either, or not, adapted to OPF. Finally, in vitro degradability of organic matter was determined using cellulase. Results showed that longer colonization was associated with higher dry matter (DM) losses. Phanerochaete chrysosporium had the highest weight loss, whereas OPF colonized for 9 wks with Ceriporiopsis subvermispora, Pleurotus ostreatus, Phlebia brevispora, Lentinula edodes, Pleurotus eryngii and Trametes versicolor had the highest lignin(pm) degradation. Treatments with the highest lignin(pm) loss, rather than selective lignin(pm) degradation, had the most potential to increase in vitro gas or volatile fatty acid production. Nevertheless, total lignin(pm) loss explained only 0.60 of the variation in in vitro DM degradability. It appeared that within the selected group of fungi which had the highest lignin(pm) degradation (i.e., C. subvermispora, Ganoderma lucidum, L. edodes, P. brevispora and P. eryngii), additional cellulose degradation was essential to substantially increase in vitro DM degradability either with rumen fluid adapted, or not, to OPF. C. subvermispora (3 wks) and L. edodes and P. brevispora (9 wks) were most promising for OPF pre-treatment, but relatively high biomass losses during fungi colonization need further research attention.
Stability of fatty acids during wilting of perennial ryegrass (Lolium perenne L.): effect of bruising and environmental conditions
Khan, N.A. ; Cone, J.W. ; Fievez, V. ; Hendriks, W.H. - \ 2011
Journal of the Science of Food and Agriculture 91 (2011)9. - ISSN 0022-5142 - p. 1659 - 1665.
light-dependent degradation - cutting date - lipid-metabolism - senescence - cultivar - forages - silage - additives - pigments - interval
BACKGROUND: Oxidation of fatty acids (FA) during field wilting of herbage could cause extensive losses of polyunsaturated FA. Recent studies showed a variable effect of wilting on the losses of FA. This suggests that environment and management conditions influence the loss of FA during wilting. The present study investigated the stability of FA in untreated and mechanically bruised perennial ryegrass, wilted under field conditions for 0, 12, 24, 36 and 48 h, or wilted under controlled climate conditions at three temperatures (15, 25 or 35 °C) and two light (dark or light) regimes to dry matter (DM) contents of 425, 525 or 625 g kg-1. RESULTS: During 48 h of field wilting, the total FA content declined (15.2 to 11.9 g kg-1 DM) consistently, despite an increase in herbage DM content (197 to 676 g kg-1). Under controlled climate conditions, the herbage total FA content declined (15.1 to 11.7 g kg-1 DM) mainly during the prolonged (56 to 62 h) initial drying to a DM content of 425 g kg-1 and did not decline with further drying to DM contents of 525 and 625 g kg-1. The decline in total FA was associated with a parallel decline in C18:3 content under field (9.15 to 6.36 g kg-1 DM) and controlled (9.12 to 6.15 g kg-1 DM) conditions. Concomitantly, the proportion of C18:3 in total FA decreased, whilst the proportion of C16:0 and C18:0 increased. Lower losses of FA (P <0.05) were observed at 15 °C compared to 25 and 35 °C. Light did not affect the losses of FA during wilting. CONCLUSIONS: The duration of the wilting period mainly affected the changes in FA content and composition. Stability of FA in herbage could be increased by minimising the duration of wilting.
|Causes of variation in fatty acid content and composition in grass silages
Khan, N.A. ; Cone, J.W. ; Fievez, V. ; Hendriks, W.H. - \ 2011
In: Proceedings of the 8th International Symposium on the Nutrition of Herbivores (ISHN8), Aberystwyth, Wales, UK, 6-9 September 2011. - Cambridge : Cambridge University Press - p. 545 - 545.
Causes of variation in fatty acid content and composition in grass silages
Khan, N.A. ; Cone, J.W. ; Fievez, V. ; Hendriks, W.H. - \ 2011
In: Proceedings of the 36th Animal Nutrition Research Forum - A platform to present Animal Nutrition Research in Belgium and the Netherlands, Leuven, Belgium, 19-04-2011. - Heverlee : Faculteit Bio-ingenieurswetenschappen, K.U. Leuven - p. 73 - 74.
The effect of silage and concentrate type on milk fatty acids and the occurrence of subacute ruminal acidosis in dairy cows
Colman, E. ; Vlaeminck, B. ; Abrahamse, P.A. ; Dijkstra, J. ; Fievez, V. - \ 2011
In: Proceedings of the British Society of Animal Science and the Association of Veterinary Teaching and research Work, Nottingham, 4-5 April 2011. - Cambridge : Cambridge University Press - p. 205 - 205.
The effect of allocation frequency in rotational grazing systems on the fatty acid profile in milk fat of dairy cows
Vlaeminck, B. ; Abrahamse, P.A. ; Fievez, V. ; Lourenco, M. ; Dijkstra, J. ; Tamminga, S. - \ 2010
In: 23th General Meeting of the European Grassland Federation, Kiel, Germany, 29 August - 02 September, 2010. - Duderstadt : Mecke Druck und Verlag - p. 102 - 102.
Four Holstein cows were used to evaluate the effect of allocating cows every 4 day (d) to a new 0.5-ha plot of Lolium perenne L. on the profile of fatty acids (FA) in milk. The experiment was run during 2 rotations with 2 measuring periods of 4 d each. During the 4 d period, the proportion (g per 100 g FA) of 18:3n-3 and total FA content (mg per g DM) of grass decreased linearly. Similarly, milk FA composition was largely affected by day within the 4 d period. Proportions of t11-18:1 in milk fat increased on d 2 (4.52 g per 100 g FA) and decreased thereafter (3.77 g per 100 g FA on d 4). Proportions of c9t11-18:2 (2.36 and 1.83 g per 100 g FA), t11c15-18:2 (0.81 and 0.63 g per 100 g FA) and 18:3n-3 (0.92 and 0.88 g per 100 g FA) in milk followed the same pattern. Results from this study suggest short term variation in pasture quality during the 4 d affected milk FA composition, with a greater effect on biohydrogenation intermediates in milk fat compared with its major precursor, 18:3n-3.